JP6888323B2 - Vehicle downhill speed control device - Google Patents

Description

The present invention relates to a vehicle downhill speed control device that automatically brakes a vehicle traveling on a downhill road to maintain a target vehicle speed.

Conventionally, there has been known a board descent speed control device (so-called hill descent control) that automatically brakes a vehicle traveling on a downhill road to keep the actual vehicle speed at the target vehicle speed (see Patent Document 1 below). ..

In such a board descending speed control device, the downhill slope of the traveling road surface is equal to or higher than a predetermined gradient, the vehicle speed is within a predetermined range, and the accelerator and brake are not operated during the descent with the control start switch turned on. When all of the above conditions are satisfied, the control is started with the vehicle speed at the time when these conditions are satisfied as the target vehicle speed. Then, during control, the target vehicle speed can be appropriately changed by operating the accelerator and the brake. For example, when it is desired to increase the target vehicle speed, the vehicle speed is increased to a desired vehicle speed by operating the accelerator and the pedal operation is stopped, and the vehicle speed at that time is set to a new target vehicle speed. The same applies when decelerating the target vehicle speed. When the vehicle is decelerated to the desired vehicle speed by the brake operation and the pedal operation is stopped, the vehicle speed at that time is set to the new target vehicle speed.

Japanese Patent No. 5169565

By the way, the slope of the traveling road surface is not always constant. Then, the driver's perceived speed changes depending on the magnitude of the downward slope of the traveling road surface. For example, if the downhill slope of the running road surface becomes steeper while driving on a downhill road, the vehicle speed feels faster at the target vehicle speed up to that point, but if the downhill slope of the running road surface becomes gentle, until then. It is possible that the vehicle speed feels slow at the target vehicle speed of. Therefore, the driver needs to change the target vehicle speed by operating the accelerator and the brake pedal in response to the change in the road surface gradient, such as when the slope of the traveling road surface changes suddenly. However, on mountain roads where the slope changes a lot, the pedal operation is required every time the road surface slope changes, which complicates the driving operation and makes it difficult for the driver to concentrate on the steering wheel operation, etc. There was room for improvement because there was no situation.

The present invention has been made in view of the above circumstances, and when the downhill speed is controlled, the target vehicle speed of the vehicle is automatically increased or decreased according to the change in the slope of the traveling road surface, and the drivability at the time of downhill is maintained. It is to provide a downhill speed control device for vehicles capable of this.

The vehicle descending speed control device of the present invention controls the vehicle so that the vehicle speed matches the target vehicle speed when descending a slope satisfying a predetermined condition, and whether the slope of the traveling road surface has changed by a predetermined amount or more. When the gradient change determining means for determining whether or not the vehicle has a gradient change determining means determines that the gradient of the traveling road surface has changed by a predetermined amount or more, the target vehicle speed is determined to change the target vehicle speed according to the amount of the gradient change. The target vehicle speed determining means includes means, and when the downward slope of the traveling road surface changes by a predetermined amount or more in a direction of increasing the downward slope, the target vehicle speed is decelerated by a predetermined speed from the target vehicle speed before the slope change. When the vehicle speed is changed and the downward slope of the traveling road surface is changed by a predetermined amount or more in a direction of becoming smaller, the target vehicle speed is changed to a speed increased by a predetermined speed from the target vehicle speed before the slope change. And.

Further, the predetermined speed that is increased or decreased by the target vehicle speed determining means may be set so as to increase as the amount of change in the gradient increases.

Further, the downhill speed control device of the vehicle is a prediction means for predicting whether or not there is a slope change portion where the slope of the traveling road surface changes by a predetermined amount or more within a predetermined distance in the traveling direction of the vehicle, and the prediction. When it is predicted that the gradient change portion is within a predetermined distance by the means, the vehicle speed deceleration means for temporarily decelerating the vehicle speed of the vehicle until the predicted gradient change portion is passed is provided. Is also good.

Further, the speed decelerated by the vehicle speed deceleration means is variable according to the actual vehicle speed and the target vehicle speed at that time, and may be set so as to increase as the actual vehicle speed and the target vehicle speed increase.

According to the present invention, since the target vehicle speed of the vehicle is appropriately changed in response to the change in the slope of the road surface during the downhill speed control, the downhill speed control of the vehicle capable of maintaining drivability during the downhill speed control. Equipment can be provided.

The figure which shows an example of the schematic structure of the vehicle which concerns on 1st Embodiment of this invention. A map showing an example of the relationship between the target vehicle speed and the gradient according to the same embodiment. The flowchart which shows an example of the vehicle speed control executed by the control device which concerns on the same embodiment. The flowchart which shows a part of an example of vehicle speed control executed by the control device which concerns on 2nd Embodiment of this invention. The flowchart which shows the other part of the example of the vehicle speed control which concerns on the same embodiment. The figure for demonstrating an example of the prediction method of the gradient amount change of the traveling road surface which concerns on this embodiment. The figure for demonstrating an example of the prediction method of the gradient amount change of the traveling road surface which concerns on this embodiment. The figure for demonstrating an example of the prediction method of the gradient amount change of the traveling road surface which concerns on this embodiment.

Hereinafter, each embodiment of the present invention will be described with reference to the drawings.
(First Embodiment)
FIG. 1 is a diagram showing an example of a schematic configuration of a vehicle 1 according to the present invention. As shown in FIG. 1, the vehicle 1 includes an ECU (Electric Control Unit) 11, an HDC (Hill Descent Control) switch 12, a meter 13, an ASC (Active Stability Control) -H / U14, and an acceleration, which are downhill speed control devices. It includes a sensor 15, a brake pedal 16, four wheel brakes 16a to 16d, four wheels 17a to 17d, a camera unit 18, and a sensor unit 19. Further, the ECU 11 and the HDC switch 12, the meter 13, the acceleration sensor 15, the camera unit 18, and the sensor unit 19 are each connected by a control line. The brake pedal 16 is connected to the ASC-H / U14. The vehicle 1 also includes other devices for realizing the function as a vehicle, but illustration and description thereof will be omitted.

The ECU 11 is a control device composed of a CPU, a ROM, a memory, and the like, and comprehensively controls each configuration of the vehicle 1. For example, the ECU 11 controls (HDC) the traveling speed of the vehicle 1 when descending a slope so as to match the target vehicle speed. Since the control for accelerating or decelerating the vehicle 1 to match the target vehicle speed is the same as the conventional control, detailed description thereof will be omitted.

The HDC switch 12 is a switch that turns on / off the HDC control. The HDC switch 12 is arranged at a position within the reach of the driver when the driver is located in the driver's seat, and is turned ON / OFF by the driver, for example.

The meter 13 informs the current actual vehicle speed of the vehicle 1. The driver grasps the actual vehicle speed of the vehicle 1 by checking the numerical value notified to the meter 13.

The ASC-H / U14 gives a braking instruction to the wheel brakes 16a to 16d for braking the wheels 17a to 17d, respectively, based on the instruction from the brake pedal 16, and automatically controls the engine (not shown) output.

The acceleration sensor 15 detects the amount of acceleration of the vehicle 1 in each of the vertical direction, the left-right direction, and the front-rear direction. The detection result is output to the ECU 11.

The brake pedal 16 instructs the ASC-H / U14 of the braking amount according to the amount of depression depressed by the driver.

The camera unit 18 includes a camera and an image processing unit. The camera is provided, for example, between the driver's seat and the passenger seat in the vehicle interior of the vehicle 1 and on the upper side, and is installed so as to be able to photograph the traveling road surface on the lower front side of the vehicle 1 via the windshield. The camera outputs the captured image data to the image processing unit. The image processing unit analyzes the image data received from the camera, determines whether or not there is an obstacle on the traveling road surface of the vehicle 1, and outputs the determination result to the ECU 11.

The sensor unit 19 is configured by providing, for example, three distance sensors including a radar and a receiving unit. Each radar is installed on the lower side of the front surface of the vehicle 1, for example, near the bumper, and emits radio waves in three different directions on the lower front side of the vehicle 1. Each receiver receives the reflected wave of the radio wave radiated from each corresponding radar. The receiving unit measures the distance based on the received reflected wave. The sensor unit 19 outputs each measured three distances to the ECU 11. Details of the method for measuring each distance will be described later with reference to FIGS. 5 to 7. The camera unit 18 and the sensor unit 19 are used in the second embodiment described later, and are not essential configurations in the first embodiment.

Next, a method of calculating the target vehicle speed when traveling downhill will be described. FIG. 2 is a diagram for explaining a specific example of the calculation method of the target vehicle speed.

The map shown in FIG. 2 (hereinafter referred to as graph g) shows the relationship between the gradient (%) and the target vehicle speed (km / h). The reference value R is obtained based on the actual vehicle speed of the vehicle 1 obtained at the start of HDC control and the gradient obtained from the acceleration sensor 15. In the present embodiment, the reference value R is obtained from the HDC control start vehicle speed / HDC control start gradient. The target vehicle speed is, for example, when the change in the amount of gradient is −Δg, the reference value R1 (> reference value R) is obtained for the target vehicle speed based on the graph g, and the change in the amount of gradient is + Δg. A reference value R2 (<reference value R) is obtained for the target vehicle speed based on the graph g. In the present embodiment, the case of obtaining by the graph g will be described, but the present invention is not limited to this, and may be obtained by another method. In the vehicle 1, the speed control is executed so as to match the target vehicle speed obtained based on the gradient in this way.

Next, the vehicle speed control executed by the ECU 11 when traveling downhill will be described. FIG. 3 is a flowchart showing an example of vehicle speed control during downhill traveling executed by the ECU 11. This process is always executed while the vehicle 1 is traveling downhill.

The ECU 11 determines whether or not the HDC switch 12 is ON (ST101). When it is determined that the HDC switch 12 is ON (ST101: YES), the ECU 11 determines whether or not the HDC control start condition is satisfied (ST102). In the present embodiment, the HDC control start condition is that the ECU 11 controls the HDC when three conditions are satisfied: the accelerator pedal (not shown) is OFF, the brake pedal 16 is OFF, the road surface gradient is equal to or higher than the predetermined speed, and the vehicle speed is lower than the predetermined vehicle speed. It is judged that the start condition is satisfied.

When it is determined that the HDC control start condition is satisfied (S102: YES), the ECU 11 determines whether or not the flag F setting is 0 (ST103). The flag F is a flag for determining whether or not the flow is the first flow in which the HDC control start condition is satisfied. The flag F is formed, for example, in a predetermined area of the memory provided in the ECU 11.

When it is determined that the setting of the flag F is zero (ST103: YES), the ECU 11 sets the target vehicle speed based on the actual vehicle speed at the start of control (when the condition is satisfied) (ST104). More specifically, when the HDC control start condition is satisfied, the actual vehicle speed at the time when the condition is satisfied is set to the initial target vehicle speed. When the ECU 11 determines that the flag F is not zero (ST104: NO), the target vehicle speed has already been set, so that the process of step ST104 is not executed and the process proceeds to the process of step ST105.

Next, the ECU 11 determines whether or not the road surface gradient has changed by a predetermined amount or more (ST105: gradient change determining means). The road surface gradient is calculated from the detection result of the acceleration sensor 15, and the change in the road surface gradient is calculated from the change in the detection result of the acceleration sensor 15. An inclination sensor may be provided instead of the acceleration sensor 15, and the road surface gradient and the change in the road surface gradient may be detected based on the detection result of the inclination sensor.

When it is determined that the road surface gradient has changed by a predetermined amount or more (ST105: YES), the ECU 11 determines whether or not the gradient has increased (ST106). In other words, it is determined whether the road surface slope has become large (sudden) or small (gentle). In the present embodiment, the determination is made based on whether or not the gradient change amount is + Δg or more. The value of Δg can be set arbitrarily.

When it is determined that the gradient has increased (ST106: YES), the ECU 11 recalculates the target vehicle speed according to the magnitude of the gradient change amount + Δg (ST107). As a result, the target vehicle speed is reduced from the current target vehicle speed. Further, when it is determined that the gradient is not large (ST106: NO), the ECU 11 recalculates the target vehicle speed according to the magnitude of the gradient change amount −Δg (ST108). As a result, the target vehicle speed is increased from the current target vehicle speed. In these recalculations of the target vehicle speed, the target vehicle speed is calculated, for example, from the map described above (see: FIG. 2). Therefore, the magnitude of the increase / decrease speed of the target vehicle speed varies according to the magnitude of the gradient change amount, and the larger the gradient change amount, the larger the increase / decrease speed of the target vehicle speed. When the target vehicle speed is recalculated in this way, the ECU 11 updates the target vehicle speed (ST109: target vehicle speed determination means). That is, the ECU 11 sets the recalculated new target vehicle speed and controls the vehicle speed so as to match the new target vehicle speed (ST111). On the other hand, when it is determined in step ST105 described above that the road surface gradient does not change by a predetermined amount or more (ST105: NO), the target vehicle speed is not changed (ST110), and the ECU 11 continues to match the current target vehicle speed. The vehicle speed is controlled (ST111). Next, the ECU 11 sets the flag F to 1 (ST112). Then, the process returns to step ST101.

On the other hand, when it is determined in step ST101 that the HDC switch 12 is not ON (ST101: NO), or when it is determined in step ST102 that the HDC control start condition is not satisfied (ST102: NO), the ECU 11 sets the flag F. Is set to zero (ST113). When the flag F is set to zero, this process ends.

As described above, the ECU 11 determines whether or not the gradient of the traveling road surface has changed by a predetermined amount Δg or more, and when it is determined that the gradient of the traveling road surface has changed by a predetermined amount Δg or more, the ECU 11 responds to the amount of change in the gradient. The target vehicle speed can be changed. Therefore, when the downhill speed is controlled, the target vehicle speed of the vehicle is automatically increased or decreased according to the change in the slope of the traveling road surface, and the drivability at the time of downhill can be maintained.

In the present embodiment, the ECU 11 changes the increase / decrease in the target vehicle speed by a predetermined amount or more in the direction in which the downward slope of the traveling road surface increases based on the map described with reference to FIG. 2, and the target vehicle speed before the change in the slope. The target vehicle speed is changed to a speed decelerated by a predetermined speed from, and when the downward slope of the traveling road surface changes by a predetermined amount or more in the direction of becoming smaller, the target speed is increased by a predetermined speed from the target vehicle speed before the gradient change. Change the vehicle speed. More specifically, the ECU 11 sets the predetermined speed so that it increases as the amount of change in the gradient increases.

(Second embodiment)
The second embodiment differs from the first embodiment in that a process of predicting a road surface portion where the slope changes and temporarily decelerating the vehicle speed in front of the road surface portion is added to the first embodiment. is there. The same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

The vehicle speed control executed by the ECU 11 when traveling downhill will be described. 4A and 4B are flowcharts showing an example of vehicle speed control executed by the ECU 11. Note that this process is always executed while the vehicle 1 is traveling downhill, as in the first embodiment.

Similar to the first embodiment, the ECU 11 determines whether or not the HDC switch 12 is ON (ST201), and when it determines that the HDC switch 12 is ON (ST201: YES), the HDC control start condition is satisfied. It is determined whether or not the flag F is set (ST202), and when it is determined that the HDC control start condition is satisfied (S202: YES), it is determined whether or not the flag F setting is 0 (ST203). When it is determined that the setting of the flag F is zero (ST203: YES), the ECU 11 sets the target vehicle speed based on the actual vehicle speed at the start of control (when the condition is satisfied) (ST204). If the ECU 11 determines that the flag F is not zero (ST204: NO), the process of step ST204 is not executed, and the process proceeds to step ST205. The processes of steps ST201 to ST204 are the same as those of steps ST101 to ST104 described above.

Next, the ECU 11 executes a gradient change prediction process for predicting a gradient change on the road surface (ST205: prediction means). The gradient change prediction process is a process of predicting whether or not there is a gradient of a predetermined amount or more ahead. A detailed description of this gradient change prediction process will be described later with reference to FIGS. 5 to 7.

Next, the ECU 11 determines whether or not there is a gradient change of a predetermined amount or more ahead based on the result of the gradient change prediction process (ST206). When it is determined that there is a gradient change of a predetermined amount or more (ST206: YES), the ECU 11 determines whether or not the current position is within a predetermined distance from the predicted gradient prediction change position (ST207). The process of step ST207 is a process that serves as a determination criterion for determining when to start decelerating the vehicle.

When it is determined that the distance is within the predetermined distance (ST207: YES), the ECU 11 maintains the vehicle speed decelerated by the predetermined speed (ST208: vehicle speed deceleration means). The predetermined speed to be decelerated here is not constant, and may be changed according to the actual vehicle speed at that time and the magnitude of the set target vehicle speed. For example, if the actual vehicle speed or the target vehicle speed is large, the predetermined speed for deceleration is large, and if it is small, the predetermined speed is set to be small.

Next, the ECU 11 determines whether or not it has passed the gradient prediction change position (ST209). If it is determined that the gradient prediction change position has not been passed (ST209: NO), the process returns to step ST208. That is, in other words, the process of temporarily decelerating the vehicle speed by a predetermined speed is continued until the gradient prediction change position is passed. Therefore, the process of step ST209 serves as a determination standard for maintaining the vehicle speed in the decelerated state until the vehicle passes the gradient change location (predicted position).

When it is determined that the vehicle has passed the gradient prediction change position (ST209: YES), the ECU 11 determines whether or not the road surface gradient has changed by a predetermined amount or more as in the first embodiment (ST210: Gradient change determination). means). More specifically, the ECU 11 calculates the amount of gradient change at the time when the vehicle passes the gradient change location (predicted position) and the gradient changes, and determines whether or not the road surface gradient has changed by a predetermined amount or more. doing.

When it is determined that the road surface gradient has changed by a predetermined amount or more (ST210: YES), it is determined whether or not the gradient has increased (ST211). When the ECU 11 determines that the gradient has increased (ST211: YES), recalculates the target vehicle speed according to the gradient change amount + Δg (ST212), and determines that the gradient has not increased (ST211: NO). The target vehicle speed is recalculated according to the amount of change in gradient −Δg (ST213), and the target vehicle speed is updated (ST214: target vehicle speed determination means).

When the target vehicle speed is updated (ST214), or when it is determined that there is no gradient change of a predetermined amount or more ahead (ST206: NO), or when it is determined that the gradient change is not a predetermined distance from the predicted gradient change distance (ST207: NO). Further, when it is determined that the road surface gradient does not change by a predetermined amount or more (ST210: NO) and there is no change in the target vehicle speed (ST215), the ECU 11 continuously controls the vehicle speed so as to match the target vehicle speed. (ST216.). Next, the ECU 11 sets the flag F to 1 (ST217). Then, the process returns to step ST201.

On the other hand, when it is determined in step ST201 that the HDC switch 12 is not ON (ST201: NO), or when it is determined in step ST202 that the HDC control start condition is not satisfied (ST202: NO), the ECU 11 is the first. The flag F is set to zero as in the embodiment (ST218). When the flag F is set to zero, this process ends.

Next, a method of predicting a change in the amount of slope of the traveling road surface when descending a slope will be described in detail. 5 to 7 are diagrams for explaining an example of a method for predicting a change in the amount of gradient. When it is confirmed that there is no obstacle based on the information from the camera unit 18, for example, the following processing is executed.

As shown in FIG. 4, it is assumed that distance sensors S1, S2, and S3 (not shown) for calculating distances for three different angles are provided in the sensor unit 19, respectively. The distance sensor S1 emits a radio wave in the traveling direction of the vehicle 1, receives the reflected wave, and measures the distance L1. The distance sensor S3 radiates radio waves in the vertical direction with respect to the traveling road surface D of the vehicle 1, receives the reflected waves, and measures the distance L3. The distance sensor S2 is a sensor for measuring the distance between the distance sensor S1 and the distance sensor S3, and more specifically, an angle A (more specifically) forming a predetermined angle with respect to the distance measured by the distance sensor S1. A radio wave is emitted in the <90 degree) direction, and the reflection is received to measure the distance L2.

Here, it is assumed that there is a gradient of an angle θ formed with respect to the traveling road surface D at a predetermined distance ahead of the traveling road surface D. Then, since the angle B is 90 degrees, it is possible to calculate the distance L4 from the intersection position of the distance L2 and the traveling road surface D to the distance L1. When the distance L4 and the distance L3 are substantially the same distance, the ECU 11 can determine that the inclination of the traveling road surface D has not changed.

Next, a method of determining a case where the change in the gradient amount of the traveling road surface D becomes smaller than a predetermined amount will be described with reference to FIG.

As shown in FIG. 5, if the distance L4 is smaller than the distance L3, it can be estimated that the inclination of the traveling road surface D becomes smaller. First, the ECU 11 calculates the change angle (change amount) θ of the inclination of the traveling road surface D. The change angle θ can be obtained as follows. The distance X1 is calculated from the angle A and the distance L2. Next, the distance X2 is calculated by subtracting the distance X1 from the distance L1. The change angle θ is calculated from the distance X2 and the distance L4. Then, when it is determined that the calculated change angle θ is equal to or greater than the angle A, the ECU 11 can determine that the inclination of the traveling road surface D is smaller than the angle A or more. In this case, the ECU 11 determines, for example, the distance ahead when the change angle θ becomes the angle A, that is, the distance calculated from the distance L2 and the change angle θ (that is, the angle A) as the predicted position of the gradient change described above. Is stored in a predetermined area in the ECU 11. The determination in step ST209 is executed using the stored predicted position.

Next, a method of determining a case where the change in the gradient amount of the traveling road surface D becomes larger than a predetermined amount will be described with reference to FIG.

As shown in FIG. 6, when the distance sensor S2 cannot receive the reflected wave, that is, when the distance L2 cannot be measured, it can be determined that the inclination of the traveling road surface D is changing in the direction of increasing the angle A or more. it can. In this case, the ECU 11 stores the distance ahead when the distance L2 cannot be measured, that is, the distance calculated from the distance L3 and the angle A as the predicted position described above in a predetermined area in the ECU 11.

The ECU 11 configured as described above predicts whether or not there is a gradient change portion where the gradient of the traveling road surface changes by a predetermined amount or more within a predetermined distance in the traveling direction of the vehicle, and there is a gradient change portion within the predetermined distance. When it is predicted, the vehicle speed can be temporarily reduced until the predicted gradient change point is passed. Therefore, it is possible to maintain drivability until the vehicle passes through the predicted downhill change point.

Further, the deceleration speed is changed according to the actual vehicle speed and the target vehicle speed at that time, and is set so that the larger the actual vehicle speed and the target vehicle speed, the larger the speed. Therefore, it is possible to further maintain the drivability until the vehicle passes through the predicted downhill change point.

In addition, the above-described embodiment is presented as an example, and is not intended to limit the scope of the invention. This novel embodiment and modification can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the gist of the invention. These embodiments and modifications are included in the gist of the invention as well as in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Vehicle, 11 ... ECU, 12 ... HDC switch, 14 ... ASC-H / U, 15 ... Accelerometer, 16a-16d ... Wheel brake, 18 ... Camera unit, 19 ... Sensor unit, D ... Driving road surface

Claims (4)

It is a vehicle downhill speed control device that controls the vehicle so that the vehicle speed matches the target vehicle speed when descending a slope that satisfies a predetermined condition.
Gradient change determining means for determining whether or not the gradient of the traveling road surface has changed by a predetermined amount or more,
When the gradient change determining means determines that the gradient of the traveling road surface has changed by a predetermined amount or more, the target vehicle speed determining means for changing the target vehicle speed according to the amount of change in the gradient.
Equipped with a,
The target vehicle speed determining means changes the target vehicle speed to a speed decelerated by a predetermined speed from the target vehicle speed before the slope change when the downward slope of the traveling road surface changes by a predetermined amount or more. When the downward slope of the traveling road surface changes by a predetermined amount or more in the direction of becoming smaller, the target vehicle speed is changed to a speed increased by a predetermined speed from the target vehicle speed before the slope change. Vehicle downhill speed control device. The vehicle descending speed control device according to claim 1 , wherein the predetermined speed that is increased or decreased by the target vehicle speed determining means is set so as to increase as the amount of change in the gradient increases. A predictive means for predicting whether or not there is a gradient change point where the gradient of the traveling road surface changes by a predetermined amount or more within a predetermined distance in the traveling direction of the vehicle.
When the prediction means predicts that the gradient change portion is within a predetermined distance, the vehicle speed reduction means for temporarily decelerating the vehicle speed until the vehicle passes the predicted gradient change portion.
The vehicle descending speed control device according to claim 1 or 2 , wherein the vehicle is provided with. Speed is decelerated by the speed reduction mechanism is variable in accordance with the actual vehicle speed and the target vehicle speed at that time, to claim 3, characterized in that the actual speed and the target vehicle speed is set to more increase larger The vehicle downhill speed control device described.

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